Ok...I think I won.
I had just enough room to pull the lines up as high as I could, and cut the old fittings off.
They were some sort of PEX fitting.
I put two 1/2" hose clamps part way down the line to keep the second hose clamps from falling down the line, then used 90deg elbows with female NPT on one end onto the shower valve, and male shark bites on the water line side. Shoved the shark bites down as far as I could, then tightened the hose clamps.
So far...no leaks.
So yeah...shark bites are my friends